Method for separating contaminants from 3-(2′-Acetoxy-Ethyl-Dihydro-2(3H)-Furanone

ABSTRACT

A process for removing impurities from 3-(2&#39;-acetoxyethyl)-dihydro-2(3H)-furanone (I), which comprises initially preparing the 3-(2&#39;-acetoxyethyl)-dihydro-2(3H)-furanone containing the undesirable impurities in a manner known per se by acetylating 3-(2&#39;-hydroxylethyl)-dihydro-2(3H)-furanone, subsequently treating it with strong mineral acids and finally removing the decomposition products of the undesirable impurities from I.

The present invention relates to a process for removing undesirableimpurities from 3-(2′-acetoxyethyl)dihydro-2(3H)-furanone of the formulaI

3-(2′-acetoxyethyl)dihydro-2(3H)-furanone is a starting material forpreparing methyl tetrahydropyran-4-carboxylate, which for its part is anintermediate in the preparation of crop protection agents.

3-(2′-Acetoxyethyl)dihydro-2(3H)-furanone is prepared, for example, byprocesses that are known per se and described, for example, in U.S. Pat.No. 5,350,863, starting from methyl acetoacetate and ethylene oxide.Another process variant by which3-(2r-acetoxyethyl)dihydro-2(3H)-furanone is obtainable is described inDokl. Akad. Nauk SSSR 27 (1940), 956-959 and U.S. Pat. No. 5,283,326.

In both variants, the desired 3-(2′-acetoxyethyl)dihydro-2(3H)-furanoneis formed as a mixture with a number of undesirable byproducts, inparticular the isomericdihydro-3-(2-methyl-1,3-dioxolan-2-yl)-2(3H)-furanone II

If I contaminated in this manner is reacted in a continuous gas phasereaction with methanol in the presence of acidic catalysts to givemethyl tetrahydropyran-4-carboxylate, considerably lower yields andshorter catalyst onstream times are obtained than when a product of highpurity without the byproducts is used. This is probably due to the factthat most byproducts contain sensitive acetal groups which decompose onthe surface of the catalyst to oligomeric and polymeric products.

The removal by distillation in particular of II from mixtures comprisingI and II can be realized only with difficulties and at high cost, owingto the boiling points, which are very close.

It is an object of the present invention to provide a process by whichundesirable byproducts, in particular II, can be removed from mixtureswith I without changing I in the process.

We have found that this object is achieved by a process for removingimpurities from 3-(2′-acetoxyethyl)dihydro-2(3H)-furanone (I), whichcomprises initially preparing the3-(2′-acetoxyethyl)dihydro-2(3H)-furanone containing the undesirableimpurities in a manner known per se by acetylating3-(2′-hydroxyethyl)-dihydro-2-(3H)-furanone, subsequently treating itwith strong mineral acids and finally removing the decompositionproducts of the undesirable impurities from I.

Surprisingly, the desired I is not degraded during treatment withmineral acids and can therefore be obtained in good yield and highpurity.

Preferred embodiments of the process according to the invention aredisclosed in the subclaims and the description below.

The process according to the invention starts with the mixture of3-(2′-hydroxyethyl)dihydro-2(3H)-furanone and undesirable impuritieswhich can be obtained by known processes which were described in theintroduction.

This mixture is initially acetylated as completely as possible.Preferred acetylating agents are acetic anhydride or acetic acid itself;in principle, however, all acetylating agents known to the personskilled in the art for corresponding acetylations are suitable. Theacetylation is generally carried out at temperatures in the range from40° C. to 200° C., preferably from 60 to 140° C., over a period of from0.5 to 10, preferably from 0.8 to 5 and in particular from 1 to 3, h.

To ensure complete acetylation, the acetylating agent is generallyemployed in a molar excess of from 5 to 50%, preferably from 5 to 20%,based on 3-(2′-hydroxyethyl)dihydro-2(3H)-furanone present in themixture.

In the subsequent step, the acetylation product is treated with strongmineral acids. Preferred mineral acids are hydrochloric acid, nitricacid and, particularly preferably, sulfuric acid. This is employedpreferably at at least 80% strength and in particular in the form ofconcentrated sulfuric acid.

The amount of sulfuric acid used can be varied within wide ranges; insome cases, it was found to be advantageous to use a molar ratio ofstrong mineral acid, based on the amount of acetylating agent used inthe preceding step, in the range of from 1:20 to 1:3, preferably from1:15 to 1:7 and in particular from 1:8 to 1:12.

For the treatment with the mineral acid, the temperature is generally inthe range of from 10 to 80, preferably from 20 to 60 and in particularfrom 30 to 50° C. The duration of the treatment is generally in therange of from 0.3 to 10, in particular from 1 to 5, h, but can, inprinciple, be varied within wide limits.

After the treatment with strong mineral acids, the decompositionproducts of the undesirable impurities, in particular ofdihydro-3-(2-methyl-1,3-dioxolan-2-yl)-2(3H)-furanone II, can be removedin a simple manner.

According to a preferred variant, the mineral acid is initiallyneutralized by addition of base, preferably aqueous alkali metalhydroxide, and the acetic acid formed as coproduct in the acetylation issubsequently, if appropriate, distilled off. Phase separation issubsequently carried out by addition of a suitable organic solvent andwater, and the organic phase is then extracted. Suitable organicsolvents are in particular aromatic hydrocarbons and especiallyalkylated benzene derivatives, such as xylene or toluene. The organicextracts are combined and the solvent is removed, and the residue canthen be rectified under reduced pressure, giving, in good yield and highpurity, the desired product, which may subsequently be processedfurther. The degree of purity of I can be increased even further bycarrying out more than one rectifications in succession. The conditionsfor the rectification are known per se to the person skilled in the artand described in the literature, so that further details are notrequired here.

After the process according to the invention has been carried out, thepurity of I is generally at least 98, preferably at least 98.5 andparticularly preferably at least 99% by weight.

The I obtainable by the process according to the invention can bereacted in a manner known per se in high yield and with good catalystonstream times to give methyl tetrahydropyran-4-carboxylate. This is animportant intermediate in the preparation of crop protection agents.

EXAMPLE 1 Comparison

In a 3.5 l pressure vessel, a mixture of 1009 g (8.7 mol) of methylacetoacetate, 1218 ml (969 g) of methanol and 110 g (0.61 mol) of a 30%strength solution of sodium methoxide in methanol was initially charged,and 765.6 g (17.4 mol) of ethylene oxide were subsequently pumped in at60° C. with stirring over a period of 8 hours. The mixture was thenstirred at 60° C. for 24 h. The reaction discharge was repeatedlyflushed with nitrogen and subsequently transferred into a stirredapparatus having an attached column. The catalyst was then neutralizedby addition of 29.6 g (0.3 mol) of sulfuric acid (96%). The low-boilingcomponents, essentially methanol, methyl acetate and methyl glycol, weredistilled off at 10 mbar (1013 Pa) up to a bottom temperature of 100° C.At 100° C., 806 g (7.9 mol) of acetic anhydride were added over a periodof one hour with stirring to the distillation residue, and the mixturewas then stirred at 100° C. for 2 h. The excess acetic anhydride and theacetic acid, which is formed as coproduct during the acetylation, weresubsequently distilled off, and the crude discharge was cooled. Afteraddition of 726 g of toluene and 300 g of water, the phases wereseparated and the aqueous phase was extracted twice with 200 ml oftoluene each time. The organic extracts were combined and the solventwas stripped off under reduced pressure using a rotary evaporator. Theresidue was rectified batchwise under reduced pressure at 10 mbar (b.p.161° C./10 mbar). This gave 1077 g (72%) of3-(2′-acetoxyethyl)dihydro-2(3H)-furanone (calculated 100%).

Composition:

3-(2′-acetoxyethyl)dihydro-2(3H)-furanone 95.0%dihydro-3-(2-methyl-1,3-dioxolan-2-yl)-2(3H)-furanone  3.5%3-(2′-hydroxyethyl)dihydro-2(3H)-furanon  0.50% others  1.0%

EXAMPLE 2 Single Batchwise Rectification

In a 3.5 l pressure vessel, a mixture of 1009 g (8.7 mol) of methylacetoacetate, 1218 ml (969 g) of methanol and 110 g (0.61 mol) of a 30%strength solution of sodium methoxide in methanol was initially charged,and 765.6 g (17.4 mol) of ethylene oxide were subsequently pumped in at60° C. with stirring over a period of 8 hours. The mixture was thenstirred at 60° C. for 24 h. The reaction discharge was repeatedlyflushed with nitrogen and subsequently transferred into a stirredapparatus having an attached column. The catalyst was then neutralizedby addition of 29.6 g (0.3 mol) of sulfuric acid (96%). The low-boilingcomponents, essentially methanol, methyl acetate and methyl glycol, weredistilled off at 10 mbar up to a bottom temperature of 100° C. At 100°C., 806 g (7.9 mol) of acetic anhydride were added over a period of onehour to the distillation residue, and the mixture was then stirred at100° C. for 2 h. To decompose thedihydro-3-(2-methyl-1,3-dioxolan-2-yl)-2(3H)-furanone, the reactionmixture was cooled to 40° C., 72.5 g (0.73 mol) of sulfuric acid (96%)were added and the mixture was then stirred at this temperature for 2hours. To neutralize the sulfuric acid, 127.5 g (1.59 mol) of 50%strength NaOH were subsequently added at 40-45° C. The acetic acid whichwas formed as coproduct during the acetylation was distilled off and thecrude discharge was cooled. After addition of 726 g of toluene and 850 gof water, the phases were separated and the aqueous phase was extractedtwice with 200 ml of toluene each time. The organic extracts werecombined and the solvent was stripped off under reduced pressure using arotary evaporator. The residue was rectified batchwise under reducedpressure at 10 mbar (b.p. 161° C./10 mbar). This gave 1056 g (71%) of3-(2′-acetoxyethyl)dihydro-2(3H)-furanone (calculated 100%).

Composition:

3-(2′-acetoxyethyl)dihydro-2(3H)-furanone 98.5%dihydro-3-(2-methyl-1,3-dioxolan-2-yl)-2(3H)-furanone  0.3%3-(2′-hydroxyethyl)dihydro-2(3H)-furanon  0.3% others  0.9%

EXAMPLE 3 Three-Fold Continuous Rectification

In a 1 m³ pressure vessel, a mixture of 348 kg (3.0 kmol) of methylacetoacetate, 420.1 l (334.2 kg) of methanol and 37.9 kg (210.3 mol) ofa 30% strength solution of sodium methoxide in methanol was initiallycharged and 264.1 kg (6.0 kmol) of ethylene oxide were subsequentlypumped in with stirring at 60° C. over a period of 8 hours. The mixturewas then stirred at 60° C. for 24 h. The reaction discharge wasrepeatedly flushed with nitrogen and subsequently transferred into a 1m3 [sic] stirred apparatus having an attached column. The catalyst wasthen neutralized by addition of 10.2 kg (103.5 mol) of sulfuric acid(96%). The low-boiling components, essentially methanol, methyl acetateand methyl glycol, were distilled off at 10 mbar (1013 Pa) up to abottom temperature of 100° C. At 100° C., 278 kg (2.7 kmol) of aceticanhydride were added with stirring over a period of one hour to thedistillation residue, and the mixture was then stirred at 100° C. for 2h. To decompose thedihydro-3-(2-methyl-1,3-dioxolan-2-yl)-2(3H)-furanone, the reactionmixture was cooled to 40° C., 25.0 kg (251.8 mol) of sulfuric acid (96%)were added and the mixture was then stirred at this temperature for twohours. To neutralize the sulfuric acid, 439.7 kg (548 mol) of 50%strength NaOH were subsequently added at 40-45° C. The acetic acidformed as coproduct during the acetylation was distilled off and thecrude discharge was cooled. After addition of 250.4 kg of toluene and293.2 kg of water, the phases were separated and the aqueous phase wasextracted twice with 100 kg of toluene each time. The organic extractswere combined and processed further. This gave 375.3 kg (73%) of3-(2′-acetoxyethyl)dihydro-2(3H)-furanone (calculated 100%).

Composition:

3-(2′-acetoxyethyl)dihydro-2(3H)-furanone 99.5%dihydro-3-(2-methyl-1,3-dioxolan-2-yl)-2(3H)-furanone <0.1%3-(2′-hydroxyethyl)dihydro-2(3H)-furanon  0.3% others  0.1%

To investigate the effects of the degree of purity of I on thesubsequent reaction, the products obtained by Examples 1 to 3 wereconverted into methyl tetrahydropyran-4-carboxylate according to thefollowing general equation:

Per hour, a solution consisting of 172 g of3-(2′-acetoxyethyl)dihydro-2(3H)-furanone and 192 g of methanol wasevaporated and passed in a tubular reactor at 250° C. over 2000 g of aγ-aluminum oxide catalyst (Pural SB™, formed into 2 mm strands, driedfor 16 h at 120° C. and calcined for 3 h at 520° C.). The gaseousreaction discharge was condensed and the resultingtetrahydropyran-4-carboxylate ester was purified by batchwisedistillation (b.p. 117° C./30 mbar).

The results of the reactions of3-(2′-acetoxyethyl)dihydro-2(3H)-furanone I with different proportionsof dihydro-3-(2-methyl-1,3-dioxolan-2-yl)-2(3H)-furanone II aresummarized in Table 1:

TABLE 1 Yield of Yield of Yield of Yield of Proportion Conver- III, atIII, after III, after III, after of II in % sion (%) the start 60 h 1200h 1440 h  3.5 (Ex.1) 100 55% 39% — —  0.3 (Ex.2) 100 68% 68% 68% 57%<0.1 (Ex.3) 100 68% 68% 68% 68%

The results of the table above show the strong effect of the content ofimpurities, in particular II, on the further processing of I.

We claim:
 1. A process for removing impurities from3-(2′-acetoxyethyl)-dihydro-2(3H)-furanone (I), which comprisesinitially preparing the 3-(2′-acetoxyethyl)dihydro-2(3H)-furanonecontaining the undesirable impurities in a manner known per se byacetylating 3-(2′-hydroxyethyl)-dihydro-2-(3H)-furanone, subsequentlytreating it with strong mineral acids and finally removing thedecomposition products of the undesirable impurities from I.
 2. Aprocess as defined in claim 1, wherein the acetylating agent used isacetic anhydride or acetic acid.
 3. A process as defined in claim 1,wherein the strong mineral acid used is sulfuric acid.
 4. A process asdefined in claim 1, wherein the treatment with sulfuric acid is carriedout at temperatures of from 20 to 70° C.
 5. A process as defined inclaim 1, wherein the decomposition products are removed by phaseseparation, subsequent extraction and distillation or rectification. 6.A process as defined in claim 5, wherein a multi-step distillation orrectification is carried out.